Although the cause of multiple Sclerosis (MS) remains unknown, there is strong evidence that demyelination and inflammation are mediated by a 7 cell autoimmune mechanism. Since CD4 7 ceils are important in the etiology and pathogenesis of MS, the mechanisms by which these cells become activated are crucial to understanding and treating demyelinating diseases. This proposal examines the role of calpain, a calcium-activated neutral proteinase, in activation of peripheral blood mononuclear cells (PBMC) cultures. One important factors involved in T cell activation is a transcription factor, nuclear kappa B (NFkB). The activation of NFicB promotes interleukin-2 (IL-2) synthesis, CD25 expression, T cell proliferation, and T cell survival, It has been suggested that NFB is activated by neutral proteinase(s) -calpain may be one such participant. Calpain has been shown to be involved in T cell proliferation and integrinmediated cell migration. Also, in demyelinating diseases (i.e., MS), the content and activity in inflammatory cells, such as CD4+ T cells, is significantly increased. From these findings, we propose the following hypotheses: (I) Calpain has a central mle in the activation of PBMCs, degradation of IkBa, and activation of NFkB promoting IL-2 synthesis; (II) Calpain activity and expression may be altered in PBMC and myelin basic protein (MBP) -specific T cells of MS patients during the course (relapse and remission) of the disease; (HI) Released calpam from activated MBP-specific T cells may contribute to epitope spreading and demyelination. These specific aims will be used to investigate these goals: (1) Examine and characterize the role that calpain plays in IL-2 synthesis and CD25 expression; (2) Examine 1KB degradation and NFkB activation and characterization of calpain interaction with 1KB in normal PBMCs; (3) Measure the expression and activity of calpain in PBMCs of MS patients and the susceptibility of these cells to calpain inhibition; (4) Measure the expression and activity of calpain in MBP-specific T cells of MS patients and the ability of calpain to produce immunogenic peptides from intact human MBP. Understanding the mechanisms involved in T cell activation and proliferation and the progression of demyelination may help to develop therapeutic strategies for the treatment of MS.